Rainbow-like reflection in cam?

[Kicker0927]

Anyone have any ideas what might be causing this rainbow-like reflection on my cam? The last picture is when I take my CPL filter off...the rainbow seems to disappear, but then the shine off my dash and accessories is more noticeable. Any suggestions?

Using Viofo A129 Duo

 

[Dashmellow]

You are seeing a phenomenon called birefringence.

The tint or glass tempering on your windshield is acting like a polarizer and is interacting with your CPL (circular polarizer), so its being polarized twice....a polarized camera looking through a polarized windshield.

The same thing will happen if you look through your windshield while wearing polarized sunglasses.

See THIS link for a full explanation and also check out the Wikipedia link above.

The solution will require removing the CPL from your camera and, if you still want to eliminate reflections you will likely need to switch to a black dash mat.

 

[IAmATeaf]

You could try rotating the CPL filter either side to see if it makes things any better or worse?

 

[jokiin]

You could try rotating the CPL filter either side to see if it makes things any better or worse?

won't help if his window is tinted, any rotation you do to reduce the rainbow effect is also going to stop the CPL doing what we want it to do (remove dashboard reflections)

 

[kamkar]

If kicker have a supported vehicle i would go strait for a dashmat in black, i run both CPL and dashmat in my car, but as i have a marginal little Suzuki car i had to make my own dashmat.
And it don't look good but it do the job just fine Vs the semi glossy charcoal grey plastics of my dashboard.